Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, plasticizers, and polymers such as nylon-6.
Currently, a common route for the production of phenol is the three-step Hock process via cumene. This first step of this process involves alkylation of benzene with propylene in the presence of an acidic catalyst to produce cumene. The second step is oxidation, preferably aerobic oxidation, of cumene to the corresponding cumene hydroperoxide. The third step is the cleavage of the cumene hydroperoxide in the presence of heterogeneous or homogeneous catalysts into equimolar amounts of phenol and acetone, a co-product. However, the world demand for phenol is growing more rapidly than that for the acetone co-product. In addition, the cost of propylene is generally high.
Thus, a process that avoids or reduces the use of propylene as a feed and coproduces higher ketones, rather than acetone, may be an attractive alternative route to the production of phenol. In addition, there is a growing market for cyclohexanone, which is used as an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam, and nylon-6.
Phenol and cyclohexanone can be co-produced by a variation of the Hock process in which cyclohexylbenzene is oxidized to obtain cyclohexylbenzene hydroperoxide, which, in turn, is decomposed in the presence of an acid catalyst to the desired phenol and cyclohexanone in a process termed “cleavage.”
WO 2010/074779 discloses that cyclohexylbenzene hydroperoxide can be produced by aerobic oxidation of cyclohexylbenzene in the presence of a catalyst. Due to reaction condition constraints, the oxidation product normally comprises a significant amount of cyclohexylbenzene. It has been found that in the cleavage reaction of cyclohexylbenzene hydroperoxide, a relatively low concentration of cyclohexylbenzene in the reaction medium is conducive to reduced side reactions, hence higher yield of desired products, i.e., cyclohexanone and phenol. This calls for the removal of cyclohexylbenzene from the oxidation product. Given the high boiling points of cyclohexylbenzene and cyclohexylbenzene hydroperoxide, and the thermal instability of cyclohexylbenzene hydroperoxide, concentrating a cyclohexylbenzene hydroperoxide mixture is not an easy undertaking.